求助一道逻辑题

shihouli123UID: 3229882

题干看懂了，有两个选项看不懂。

shihouli123UID: 3229882

答案为...

crazyrobinUID: 2368627

哪个选项看不懂？

shihouli123UID: 3229882

crazyrobin 发表于 2013-5-24 17:03
哪个选项看不懂？

BD 你能讲解一下这道题吗

shihouli123UID: 3229882

答案为A

crazyrobinUID: 2368627

unless的意思是 if not
这题core argument是
if not bad weather/ if not too few tickets being sold ---------------> concert will go on
取一下contrapositive(逆否命题)
concert being cancelled ------------------> bad weather and too few tickets being sold.
and
concert cancelled ------> refund made to the buyer

现在说 some people has got refund, 首先 some是一个非常vague的 modifier
某些人收到了refund 并不一代表concert被cancel
所以bad weather/ too few tickets 都未必会发生
这个逻辑错误是reverse logic
因为 buyers get refund无法推出 concert being cancelled, 而所谓的 weather, ticket numbers 都是 cancelled的结果
A的意思就是讲reverse logic

A--------->B 那么a叫做 sufficient condition, B叫做 necessary condition
答案A说的是A---------->B这个argument里面，B发生了，也就是necessary condition appears，带着并不代表一定是A发生，因为可能有其他因素，也就是其他的sufficient条件。

B的意思是需要2个sufficient condition, 但现在只有一个，但是这题的logic flaw是 reverse logic
D的意思是某些东西在某种条件下无法发生，那么他永远不会发生，这是另外一个经典logic flaw也就是 absence of proof = proof of absence
找不到证据 = 证据不存在

Let me know if you have any questions

MaxFeburarybirdUID: 3023313

crazyrobin 发表于 2013-5-24 04:44
unless的意思是 if not
这题core argument是
if not bad weather/ if not too few tickets being sold - ...

"取一下contrapositive(逆否命题)
concert being cancelled ------------------> bad weather and too few tickets being sold."
CR，你的回答里这句话感觉有点问题，应该是 concert being cancelled ---> bad weather or too few tickets being sold

if not "bad weather or too few tickets" 是 "bad weather or too few tickets" 的否命题，所以和 "not bad weather and (注意是 and) not too few tickets sold" 是相等的。。。所以，这个命题的否命题就该是 “bad weather or (这里是 or) too few tickets sold”

所以联系起来，整个你否命题就该是“concert being cancelled ---> bad weather or too few tickets being sold”

MaxFeburarybirdUID: 3023313

crazyrobin 发表于 2013-5-24 04:44
unless的意思是 if not
这题core argument是
if not bad weather/ if not too few tickets being sold - ...

其他解释感觉都没啥问题，就是刚开头的小问题~~~

crazyrobinUID: 2368627

MaxFeburarybird 发表于 2013-5-25 06:22
"取一下contrapositive(逆否命题)
concert being cancelled ------------------> bad weather and too f ...

哦对的
这个用
A or B( or both) -------> C来看contrapositive最简单了
~C ------> ~A or ~B
但是如果A、B是exclusive的话，那么就变成了 ~C-------> ~A and ~B